Affiliated Companies
  
See Affiliate Network.
This is a tricky term, as it could have multiple but equally accurate definitions. "Affiliated companies" could simply refer to firms that have some business relation to each other, and these definitions vary from country to country, or even agency-to-agency (i.e., IRS v. SEC). But generally the term refers to voting-power ownership, whereby affiliated companies either own part, or are partly owned, by each other.
If Vito's Equipment, Inc. owned 20% of Sonny's Contracting Co., and 51% of Mikey's Demo Corp., but had no ownership in Connie's landfill, the former three would be considered "affiliated companies" (with Michael's being further classified as a "subsidiary"), while the landfill would be unaffiliated.